Production of aromatic tar



C. T. STEELE ETAL PRODUCTION OF AROMATIC TAR Sept. 25, 1956 Filed April 20, 1951 2 Sheets-Sheet o m4@ 25N;

Sept' 25, 1956 c. T. STEELE ErAL 2,764,527

PRODUCTION 0F AROMATIC TAR Filed April 20, 1951 2 Sheet's-Sheet 2 'GAS-SLNE LIGHTER Dls-VILLATioL) Tow/EQ no ya l 08 SEPAQATOQ @RUM/f -52 FLASH Daum-N 92 TQIPPHOG STEAM 98 @AQ ,o

7 EBLK f-ic0 FOQQAQE T-TI-cvf-Z LZLL' T. St, Le e @artic G. Mocepgaa flve atofs 'A f 7T' NW Clt-coinc United States Patent O PRODUCTION or ARoMATIC TAR Clellie 'I'. Steele and Carl G. Morrison, Baton Rouge, La., assignors to Esso Research and Engineering Company, a corporation of Delaware Application April 20, 195l'1, Serial No. 222,002 I l s Claims. `(ci. 19t-49) of gas oils followed by thermal cracking of a heavy cat' alytic oil fraction at conditions conducive to the formation of an aromatic tar having gravity `and-sediment characteristics suitable for the production of high quality furnace black useful in rubber compounding. `Theinvention also contemplates the production of such high quality furnace black by means of -this process.

In conventional petroleum refining. the crude .petroleum is rst distilled to produce, in addition to other=products, distillate fractions which may be converted into motor fuels by suitable refining processes. Catalytic cracking is the most important and most widely usedfof these reining processes because it produces high octanegnumber gasoline from higher boiling crudedistillates. The thermal and procedural requirements of catalytic cracking have been met most eiciently by the so-calledzfluid cat' alyst technique wherein finelyv divided catalystfis continuously circulated betweenf'afcracking zone andza` com- The production capacity of plants of this type is limited by their carbon burning capacity and thus by the carbonforming vtendency of the feed stock. Feed stocks having a strong carbon-forming tendency are, therefore, undesirable.

While most virgin gas oils areunobjectionable in this respect, the situationy is complicated by` the fact that the cracking reaction yields, in addition to motor fuel range and lighter products, substantial proportionsl of'up to about 30-50% on feed, of higher boiling fractions, such as gas oils and heavier materials boiling above 450 up to 800 F. or higher. These materials are of ai considerably lower value than motor fuels and vmustbe extensively further converted into motor fuels to maintain a sound economical balance of the process.

limited value because these so-called cycle oils"fare quite generally much stronger carbon formers than Virgin gas oils, their carbon-forming tendency being the stronger the higher their boiling range.

Heretofore, it has been proposed to alleviate these" diiculties by subjecting cycle oils, particularly the higher boiling cycle oils to thermal cracking to produce additional amounts of gasoline and other valuable distillate fractions, in which coke formation is no serious problem.

However, this procedure is complicated byother;` diili v A Recycle to. the cracking stage, though widely practiced, is only of late oils-'by thermal cracking of -catalytic cycle oils.

2,764,527 Patented Sept.`v4- 25, 195.6

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2. culties. By far the largest proportion of the thermal cracking product is'recovered-in the form of a heavy tar of the fuely oil boilingrange amountingvto more than 470 vol. on thermal crackingfeed.` It` is essential that this vhigh' proportion of the product have a considerable commercial value to make the operation economically feasible. Since the commercial value of thel lighter products, particularly the gasoline. fractions, is by farhigherthan the value of the tar for` any purpose known at present it is, however, necessary, to reducetar production in favor of gasoline production as much as possible. This may be accomplished by increasing the severityof the thermal cracking reaction, particularly with respect to temperature so as to convert morey of the-feedto lighter distillates. Thus, tar production maybe reduced to 50.vol.A percent or thereabout with a corresponding increase in distillate yields.l However, the more `severethecrackingreaction, the poorer is the qualityof the tar as a-fuel oil. In addition, it has not beenl possible heretofore to p-roduce at these-high severity` thermal cracking conditions from a catalytic cycleoil a thermally cracked tar useful for the production ofv high'. quality furnace black suitable for rubber compounding, without a serious reductionin distillate yields. The present invention overcomes this diculty. f

lt is, therefore7 the principal object of the present invention to provide an improved process for the production of a high quality tar and relatively large amounts of distil- A more specific object of the inventionis a` process for producing high quality furnace black with the aid of a procedure of the type specified. Other :and more specific objectsand advantages of the invention Ywill appear from the following description of the invention wherein reference will be made to theaccompanying drawing in which Figurel is a schematical ilow plan of a system suitable to carry out a preferred embodiment of the invention;

and

- Figure 2 is a similiar illustration of a modification o the system shown in Figure l.

Ithas now been foundthat thermally cracked tars of excellent qualities, particularly for the purpose of high vquality furnace black manufacture as well 'as high yields of distillate'oils, may be produced by thermally cracking catalytic cycle oils, particularly so-calledv clarified oils which represent theheaviest fractions of catalytic cycle oils, at carefully controlled specific conditions, particularly at carefully controlled temperatures, in all sections of the thermal crackinglunit.` Such units normallycomprise a tired cracking coil discharging 4into a Vapor-liquid separator, bottoms of which are ashed and steam stripped in a flashing zone.'v Overhead 'from the separator and flashingy zone` represents the distillate product. Flash Insystems of this type using cracking coils and soaking drums, conditions in accordance with the present inventionr include cracking coil pressures of about .300#600-13. s. i. g., cracking coil outlet temperatures of 935 f-'950 F., cracking zone throughputs of about 6-16 volumes of cold oil per volume of coil cracking space per hour v./v./hr.) which corresponds to about 0.5-1.2 v./v./hr. based on coil plus soaker space, separator pressures of about -100 p. s. i. g., separator temperatures of 800-820 F; in the top and 790-810 F. in the bottom, flash zone pressures of about atmospheric to 1.0 p. s. i. g. and flash zone temperatures of'j'ust about 730 F. in the top arid`570iFfin the bottom; At these conditions about 45` vol. of Avaluable distillate oils and 45 vol. %f" of Y tar are produced, 'on fthe" basis* of" catalytic cycle oil charged to the thermal cracking stage. The tar has the following inspections:

Gravity, API 0-3. Sediment by extraction (ASTM-D-473) 0.2 maximum. H/C atomic ratio 1.0-1.1. Viscosity, SSU at 210 F 50-90. Flash point,F 215 minimum.

The aromaticity of this tar is shown by its deficiency in hydrogen. This value is limited by the requirement of reducing coke formation in the cracking process. Coke so formed shows up in the tar as sediment by extraction which, in concentrations higher than those shown above, is a deleterious constituent in the final l furnace black product.

More specifically, the gravity, sediment and H/ C ratio must not appreciably deviate from the values given above if the tar is to be useful in the manufacture of furnace black for rubber compounding. Extensive tests have demonstrated that appreciable variations of the conditions specified above prevent the production of tars complying with these requirements. For example, if the oil is thermally cracked at more severe conditions, particularly at higher temperatures and flashed and stripped less completely, the resulting gravity of the tar will be satisfactory, but the asphaltene content will be too high. Asphaltenes are those constituents of the tar which are insoluble in low molecular weight parailns. These materials are diicult to vaporize in conventional carbon black manufacture and appear in the product carbon black in the form of large size unconverted aggregates. If the oil is cracked less severely and flashed and stripped more completely, the-gravity will be again satisfactory but the H/C atomic ratio will be too high, i. e., aromaticity will be too low. Other variations in the process conditions create different but equally prohibitive variartions in the tar properties.

Having set forth its objects and general nature, the

illustrated therein comprises a iluid catalytic cracking unit 3 and a single stage thermal cracking unit 30, both of essentially conventional design, details of construction having been omitted for the sake of simplicity. The function 4and coactionof these elements for the purpose of this invention Will be forthwith described.

In operation, a virgin gas oil which may have a boiling range kof about 620-950 F. is passed through line 1 to catalytic cracking unit 3 wherein it is subjected to fluid-type catalytic cracking at conventional conditions in a manner known per se. Briefly, operations of this type involve the use of finely divided catalysts such as various activated clays or composites of silica gel with alumina, magnesia and/or boria, particularly silica gelalumina composites containing about 13% of AlzOs and ,having a particle size of about 50-400 mesh, mostly about l100-200 mesh. The catalyst is maintained in separatecracking and regenerating Vessels in a dense, turbulent, tluidized lstate by gasiform media passing upwardly through the beds at linear superficial velocities of about 0.3-2.5ft. per second. The catalyst circulates.,

continuously between the reactor and regenerator, heat for cracking being generated by burning carbon from the catalyst in the regenerator. Conventional conditions include cracking temperatures of about 800-1000 F., regeneration temperatures of about 950-1200 F., but higher than the cracking temperature, pressures from subatmospheric to 100 p. s. i. g. or higher, total oil feed rates of about 4-5 lbs. of oil per 1b. of catalyst per hour,

catalyst to oil'ratios of about 6-10 and oil recycle to fresh feed ratios of up to about 0.5 on a Weight basis. v

.Cracked vapors containing small amounts of entrained catalystare vpassed` from the cracking reactor of unit` 3 through line 5 to a conventional product distillation tower l7 from which catalytic gasoline and heating oil fractions may be recovered via lines 9 and 11, respectively. A light cycle oil having a boiling range of about 620-700 F. and amounting to about 15-35 vol. percent, on virgin gas oil feed may be recycled via line 13 to the cracking reactor of unit 3. Tower bottoms boiling above 700 F. and amounting to about 2.0-10 vol. percent on virgin gas oil feed, are withdrawn via line 15 to a settler 17 wherein this oil is separated into a lower layer containing a slurry of catalyst iines in oil and an upper layer of clarified oil. The lower layer together with the slurried catalyst may be recycled in line 19 to the cracking reactor of unit 3 at a rate of about 0.8-4.0% on fresh feed. The upper layer, i. e. the clarified oil, is withdrawn through line 21. This oil which may have a gravity of about 17-20 API is further treated in accordance with the invention as follows.

Line 21 discharges into an intermediate portion of a product distillation tower 23 which serves the work-up of the -thermally cracked distillate oils as will appear more clearly hereinafter. Distillate products including gasoline and amounting to about 0.3-0.5 vol. per vol. of feed through line 21 are recovered through line 24 at a temperature of about 380-400 F. Bottoms from tower 23 including thermally cracked recycle bottoms and amounting to about 1-3 vol. per vol. of feed through line 21 are withdrawn through line 25 at a temperature of about 570-590 F. This material which may have an API gravity of about l7-19 is supplied by means of pump 27 to conventional thermal cracking unit 30. This unit may consist of two conventional furnace coils operated in parallel and discharging into a soaking drum. The oil feed is cracked in these two coils and the soaking drum at a pressure of about S10-520 p. s. i. g., a coil outlet temperature of 935-950 F. and a total residence time corresponding to a throughput of about 0.5-1.2 v./v./ hr. through coil and soaker cracking space. Cracked eflluent from unit 30 is transferred through pressure release valve 32 to a vapor-liquid separator 34 maintained at a pressure .of about -110 p. s. i. g., a top temperature of 800-820 F. and a bottom temperature of about 790-810 F. The overhead vapors from separator 34 may be passed through line 36 to a lower portion oftower 23. This distillate may amount to about 1.3-3.5 liquid vol. per vol. of feed through line 21.

Thenbottoms of separator 34 representing the remainder of the thermally cracked product are withdrawn via line 40 andvrelease valve 42 and ashed into flash drum 44 at about atmospheric pressure. Flash drum 44 is maintained at a temperature of about 730 F. in the top and about 570 F. in the bottom. Stripping steam is introduced through line 46 into the bottom of llash drum 44 in amounts of about 1.5-3 lbs. per bbl. of tar to remove light products which are vaporized and withdrawn overhead to be condensed in line 48 and passed to a lower portion oftower 23 after water removal in any conventional manner (not shown). Light products so removed may amount to about 0.1-0.3 vol. per vol. of feed in line 21. The bottoms of llash drum 44 are recovered through line 50. This material, amounting to about 0.4-0.6 vol. per vol. of feed in line 21, is an aromatic tar which complies with the specifications set forth above for the purposes of producing furnace black suitable in rubber compound- AThe conversion of the tar into furnace black may be carried out in unit 52 in any conventional manner, for example, by burning the tar with a combustion-supporting gas using a deficiency of oxygen based on carbon in the tar, and collecting nely divided product carbon from the llue gases by means of centrifugal and electrostatic gas-solids separation.

- The system shown in Figure 1 permits of certain modilications. For example, the flash drum overhead in line 48 may be processed in a different manner to be used as such for fuel blending after water removal.

A system similar `to that of Figure 1 except for the vfact that two thermal cracking stages 62 and 80 are used in a recycle type of operation in place of cracking unit 30 is shown in Figure 2 in which the catalytic cracking stage which is identical with that described with reference to Figure 1 has been omitted in the interest of brevity.

Referring now in detail to Figure 2, the clarified catalytic heavy oil owing through line 21 is pumped by pump 60 to thermal cracking unit 62 which may be of the same construction as unit 30 of Figure 1. The cracking temperature in unit 62 is preferably held at about 900 F. at the coil outlet and a cracking pressure of about 500 p. s. i. g. is used at a total oil residence time in coil and soaker corresponding to that speciiied for unit 30 of Figure 1. The cracked eiuent istransferred through line 64 and release valve 66 to separator 68 wherein product vapors and liquid are separated substantially as described with reference to separator 34 of Figure l, overhead from separator 68 being passed via line 70 to distillation tower 74 from which distillate products may be recovered via line 76 at about 380-400 F. Bottoms from tower 74 are removed at a temperature of about 610-630 F'. and a pressure of about 80-100 p. s. i. g. through line 78 and pumped by pump 79 to the second stage thermal cracking unit 80. This unit which may be of t-he same design as unit 62 is preferably operated at a coil outlet temperature of about 950 F., a pressure of about 500 p. s. i. g. and the same oil residence time as specified for unit 62. Effluent from unit 80 is passed via line 82 and release valve 84 to separator` 68 to be treated therein together with the eiuent from unit 62.

Separator ybottoms amounting to about 0.5-0.8 vol; per vol. of feed in line 21 are withdrawn via line 86 and iiashed through release valve 88 into iiash drum 90 at atmospheric pressure. Flash drum 90 is operated at the conditions specified with reference to flash drum 44 of Figure 1, stripping steam being admitted via line 92. The

vaporous overhead from flash drum 90'. is withdrawn' via line 94 and recycled by pump 96 after suitable conventional water removal' to the rst thermal cracking unit 62 which it enters together with the feed supplied through line 21. Alternatively these vapors may be transferred to tower 74 or they may be removed for separate processing and usage as pointed out with reference to vapors flowing through line 48 of Figure 1. The tar recovered from ash drum 90 through line 98 is of adequate quality to be converted in carbon black furnace 100 into furnace black suitable for rubber compounding.

The beneficial effects of the invention will be further illustrated by the following comparative example.

Example To illustrate the superiority of the process of the invention over conventional type operations and to demonstrate the criticality of a close control and correlation of the reaction conditions within the limits of the invention, there are reported below the conditions and results of three thermal cracking runs which are representative for three types of operations each carried out for a considerable length of time on a commercial scale in a coil-and-soaker system. Run I is representative for an operation carried out in a two-stage system of the type of Figure 2 yielding a tar of relatively `high API gravity. Runs II and III are representative for operations carried out in a single-stage system with recycle of the type illustrated in Figure l, run II yielding a low API gravity tar and run III a tar of intermediate gravity, the latter run being typical for operations in accordance with the invention. The feed stock to all three runs was a clarified oil recovered from the product fractionator of a commercial uid-type catalytic cracking plant operated as described above with reference to unit 3 and tower 7 of Figure 1. The essential reaction conditions of the thermal cracking stages and the results are summarized in the table below.

Run N o- I II III Type oi Operation Figure 2 Figure 1 Figure 1 Conditions:

Coil Outlet Temp., F.:

Unit 62 895 Throughputs, v /hr (Coil-l-Soaker) (Total Feed to Coil) 0. 9 1. 0 0.8

Top Bottom Top Bottom Top Bottom Separator Temp., F 792 800 820 805 810 800 Distlllation Tower, F 390 620 360 670 390 580 Flash Drum, F- 645 590 640 470 730 570 Cat. Cracking Distillation Tower Bot- 720 713 725 toms, F Separator Bottoms:

Gravity, API 13. 5 -4. 7 6. 6 Viscosity, SUS 210 158 l 386 Inspections:

Flash Drum Bottoms:

Gravity, API 10.1 6. 8 0.5 Viscosity, SUS 210 F 50 191 179 Sediment (ASTM-D-473) 0. 2 0. 2 0. 2 'Bl/C Atomic Ratio, ea l. 5 0.85 1. 1 Flash Drum Overhead:

Gravity, API 22. 4 10. 8 15. 7 10% ASTM Distillaton, F--- 481 444 548 ASTM Distillation, F 622 636 686 ASTM Distillation, F 720 88.5 752 87. 0 750 Feed to Thermal Cracking Units.

Gravity, API 22. 4 19. 5 18.0 10% 10 mm. Vacuum Dist., F.. 264 339 357 50% 10 mm. Vacuum Dist., F 440 439 442 90% 10 mm. Vacuum Dist., F 540 555 571 Viscosity SUS F 63 90. 5 95 Yields:

Gasnwt. percent 2.17 9. 99 5. 5 Dlstillate, V01. percent. 19. 30 35. 53 45. 7 Flash Drum O. H., V01 20. 73 Tar, Vol. percent 57. 80 54. 48 54.7

1 SUS 100.

The above data show that run III Which was carried out at the conditions of the present invention yielded substantially -larger amounts of valuable distillate products and about equivalent amounts of a tar of far superior quality with respect to gravity and H/C atomic ratio or aromaticity, as compared with runs I and II which were carried out using a similar feed stock at conditions which, prior to the present invention, have been believed to be substantially equivalent to those of the present invention with respect to these properties.

Fluid catalytic cracking has been repeatedly referred to in the above description and this is the preferred method of employing the present invention because certain of the advantages afforded by the invention are peculiar to this type of catalytic cracking. For example, the advantage of disposing of heavy catalytic cycle oils without increasing the carbon load on the catalytic cracking system is by far the greatest for uid catalytic cracking. However, tars suitable for the manufacture of high quality furnace black may also be produced by thermally cracking in accordance with the invention heavy product oils from other catalytic operations, such as fixed bed, moving bed or suspensoid catalytic cracking operations or other heavy oils having similar characteristics.

The foregoing description and exemplary operations have served to illustrate specic embodiments of the invention but are not intended to be limiting in scope.

What is claimed is:

1. A process of producing aromatic tar suitable for the manufacture of carbon black, which comprises catalytically cracking a virgin gas oil to form cracked products including motor fuels, oils of intermediate boiling range and a catalytic cycle oil of relatively high boiling range, subjecting at least a portion of said cycle oil to thermal cracking at a temperature of 935-950 F. and a pressure of about 300-600 p. s. i. g., separating vaporous from liquid cracking products in a separating zone at an elevated pressure substantially lower than said first-named pressure, separately withdrawing from said separating zone vapors at a temperature of 80G-820 F. and liquid at a temperature of 790-810 F., flashing and steam stripping said withdrawn liquid at about atmospheric pressure in a flashing zone, separately withdrawing 8 from said flashing zone vapors at a temperature of about 730 F. and liquid at a temperature of about 570 F., and lrecovering said aromatic tar in the form of said last-named withdrawn liquid.

2. The process of claim 1 in which atleast a portion of said thermal cracking takes place in an externally heated narrowly confined extended path at an oil residence time corresponding to an oil throughput of about 6-16 volumes of cold yoil per volume of cracking space at cracking temperature per hour.

3. The process of claim 2 in which a portion of said thermal cracking takes place in said path, said thermal cracking being completed in an expanded soaking zone at a total oil residence time corresponding to an oil throughput 4of about 0.5-1.2 volumes of cold oil per total volume of said path and soaking zone at cracking temperature per hour.

4. The process of claim 1 in which said catalytic cracking is carried .out in the presence of a dense turbulent mass of subdivided cracking catalyst fluidized by an upwardly flowing gasiform medium.

5. The process of claim 4 in which said cycle oil is a clarified cycle oil having a gravity of about 17-20 API.

References Cited in the le of this patent UNITED STATES PATENTS Re. 22,886 Ayers June 3, 1947 1,992,752 Kershaw Feb. 26, 1935 2,198,557 De Florez et al Apr. 23, 1940 2,218,024 Eastman et al. Oct. 15, 1940 2,249,705 Eastman et al July 15, 1941 2,342,888 Nysewander Feb. 29, 1944 2,368,704 Carlson Feb. 6, 1945 2,379,966 Johnson July 10, 1945 2,516,134 Molique July 25, 1950 2,572,734 Kramer Oct. 23, 1951 2,608,470 Hellrners et al. Aug. 26, 1952 2,659,662 Heller Nov. 17, 1953 2,659,663 Heller Nov. 17, 1953 FOREIGN PATENTS i 497,377 Belgium Aug. 31, 1950 

1. A PROCESS OF PRODUCING AROMATIC TAR SUITABLE FOR THE MANUFACTURE OF CARBON BLACK, WHICH COMPRISES CATALYTICALLY CRACKING A VIRGIN GAS OIL TO FORM CRACKED PRODUCTS INCLUDING MOTOR FUELS, OILS OF INTERMEDIATE BOILING RANGE AND A CATALYTIC CYCLE OIL OF RELATIVELY HIGH BOILING RANGE, SUBJECTING AT LEAST A PORTION OF SAID CYCLE OIL TO THERMAL CRACKING AT A TEMPERATURE OF 935*-950* F. AND A PRESSURE OF ABOUT 300-600 P.S.I.G., SEPARATING VAPOROUS FROM LIQUIID CRACKING PRODUCTS IN A SEPARATING ZONE AT AN ELEVATED PRESSURE SUBSTANTIALLY LOWER THAN SAID FIRST-NAMED PRESSURE, SEPARATELY WITHDRAWING FROM SAID SEPARATING ZONE VAPORS AT A TEMPERATURE OF 800-820* F. AND LIQUID AT A TEMPERATURE OF 790*-810* F., FLASHING AND STEAM STRIPPING SAID WITHDRAWN LIQUID AT ABOUT ATMOSPHERIC PRESSURE IN A FLASHING ZONE, SEPARATELY WITHDRAWING FROM SAID FLASHING ZONE VAPORS AT A TEMPERATURE OF ABOUT 730* F. AND LIQUID AT A TEMPERATURE OF ABOUT 570* F., AND RECOVERING SAID AROMATIC TAR IN THE FROM OF SAID LAST-NAMED WITHDRAWN LIQUID. 